A vehicle such as a dump truck is used for transporting rocks, ore, gravel, etc. In such a vehicle, it is very important to exactly detect weight of a load carried on the vehicle for the purpose of preventing the load weight from exceeding the rated value.
In recent years, a vehicle-install type load meter for measuring carrying weight of a vehicle has been developed. In the vehicle-installed type load meter, force acting on each of, e.g., four suspension cylinders is calculated by multiplying hydraulic pressure in each suspension cylinder with a cross-sectional area of the suspension cylinder. Based on the total of the force acting on the suspension cylinders, the weight of the vehicle in loaded state is obtained. Then, the carrying weight of the vehicle is determined by subtracting weight of the vehicle in a vacant state from the weight of the vehicle in the loaded state.
However, in the load meter of the above type in which the force acting on the four suspension cylinders are summed to determine the carrying weight of the vehicle, a measurement error arises when the vehicle inclines in the longitudinal direction, i.e., when the road surface is inclined in the direction in which the vehicle runs.
To prevent the measurement error, the inventors of this application proposed a system for exactly determining carrying weight of a vehicle in which inclination of the road surface is successively detected by using an inclinometer and force acting on each suspension cylinder is corrected according to the value detected by the inclinometer.
In the proposed system, the carrying weight measured by the vehicle-installed type load meter is displayed on the screen of a display device mounted on the vehicle. Thus, an operator can perform work while confirming the current carrying weight on the screen of the display unit.
As causes for degrading the accuracy in measuring of the carrying weight of a vehicle, the following facts have been found. Namely, for a vehicle having a rigid type suspension system, measurement accuracy does not become degraded significantly. However, for a vehicle using suspension cylinders in the suspension system, carrying load weight acting on the front wheel side differs from that acting on the rear wheel side depending on the magnitude of the load weight. This difference arises due to the difference in supporting system for each suspension cylinder on the front wheel side and the rear wheel side. As a result, when the vehicle weight is obtained based on force acting on each suspension cylinder, the obtained vehicle weight is greatly influenced by the magnitude of the load weight, thus resulting in measurement error. The influence due to the magnitude of the load weight varies depending on manners of supporting the vehicle body to the vehicle axles using suspension cylinders.
In addition, the familiar unit in which the carrying weight is presented is often different from operator to operator. Thus, when one unit is adopted for the load weight, an operator familiar with a unit different from the adopted unit cannot exactly recognize the load weight on the vehicle.
The present invention has been made in consideration of the foregoing background. A first object of the present invention is to provide a system for measuring carrying weight of a vehicle using suspension cylinders capable of measuring load weight at a high accuracy regardless of manners of mounting the suspension cylinders on the vehicle. A second object of the present invention is to provide a system for measuring carrying weight of a vehicle capable of changing units of carrying weight so that the adopted unit is always familiar to an operator who operates the vehicle. Therefore, a measuring system according to the present invention enables operators to recognize an exact carrying weight of a vehicle.